1. Field of the Invention
This invention relates to windows in buildings. Intensity of sunlight passing through the window is automatically controlled and regulated at comfortable intensity in response to natural variations in sunlight, and is insensitive to ambient temperature. A clear undistorted view is maintained while eliminating glare.
2. Description of the Related Art
Prior art for automated window shutters may be classified by control inputs as either thermal or solar-sensitive. Temperature-sensitive thermal shutters are suitable to reduce energy costs of space heating and/or cooling. They operate without regard to interior illumination, and often distort or interfere with vision.
U.S. Pat. No. 4,261,331 for example describes a thermal shutter where a crystalline solute is precipitated from solution above a threshold temperature. Crystals suspended in the solution scatter light back out of the window and thereby regulate interior temperature. U.S. Pat No. 3,723,349 discloses a thermochromic material which also changes its color in response to temperature. Popular Science July 1993 page 83 describes "Cloud Gel" as a thermal-sensitive polymer suspension. Submicron size polymer strands aggregate when hot to scatter and reflect sunlight. The solution color appears to change from clear to white. Each of these automatic shutters reduces light penetration when the window surface becomes hot.
Solar-sensitive shutters, unlike thermal shutters, serve to regulate and control illumination at a level which is useful and comfortable, regardless of window surface or building interior temperature. This invention belongs to the latter category.
Prior art may be further classified according to control response as mechanical, electrochromic, or fluidic. The mechanical category includes powered operation of familiar window coverings which are conventionally operated by hand.
Several examples of the mechanical type are known wherein a switch actuates a motor-controlled mechanism to draw or lower a shade or shutter, actuate a blind, or by the use of cables, pulleys or gears move a curtain, shade or shutter located at the inner surface of a window. Such mechanical devices are costly, complex and trouble-prone. In addition, they may be considered unaesthetic by standards of the 1990's.
Examples of electrochromic window shutters are described for example in Popular Science of July 1993. Electro-optical materials sandwiched between transparent window panes vary their light transmission in response to a voltage imposed between the two panes. A continuous voltage supply is required to hold the shutter either open (transparent) or closed, depending on the type of technology employed. Most of these shutters interfere with the visual image through the window. All of them are too expensive for practical or widespread use. Further, their lives are limited by unwanted photochemical or electrochemical side reactions.
This invention is the only known example of an automatic fluidic window shutter.